Jauch



July 18, 1961 -H. JA'UCH 2,993,165

MEASURING APPARATUS Filed May 31, 1957 5 Sheets-Sheet 1 Fig./

IN VE N TOR July 18,- 1961 Filed May 31, 1957 H. JAUCH MEASURINGAPPARATUS 5 Sheets-Sheet 2 IN VENT OR WWW July 18, 1961 'H. JAUC'H2,993,165

' MEASURING APPARATUS Filed May 31, 1957 5 Sheets-Sheet 3 IN VEN TOR BYWJMM' July 18, 1961 H. JAUCH 2,993,165

MEASURING APPARATUS Filed May 31, 195'! 5'Sheets-Sheet 4 2 II; /l'++ E1: l I I Fi .13bllll Fig./3c|||| INVENTOR Human/M July 18, 1961 FiledMay 31, 1957 H. JAUCH MEASURING APPARATUS 5 Sheets-Sheet 5 Fig/4 47'4639 48" 2 E 'EK l3 IN VENT 0R Human/M United tates Patent 2,993,165MEASURING APPARATUS Hermann Jauch, Kornerstrasse 58, Rottweil, GermanyFiled May '31, 1957, Ser. No. 662,879 25 Claims. (Cl. '32432) Thepresent invention relates to an apparatus for electrostaticallymeasuring electric field intensity, particularly for measuring theintensity of an atmospheric electrostatic field.

Known apparatus of this type incorporate two electrically conductivecollector electrodes which are well insulated from each other and whichare connected to each other by way of a precision resistance formeasurement purposes. One disadvantage of the known apparatus is thatone side must be groundedso that the apparatus can not be freely movedin space. Moreover, existing apparatus are usually constructednon-symmetrically and for this reason have a relatively low sensitivity.In one known type of cylindrical measuring apparatus the measuringvoltage must be taken off slip rings, and this easily producesinterference and inaccuracies.

A precise determination of the actual field pattern of the atmosphericelectrostatic field pattern as a function of space and time is possibleonly when free movement of the apparatus is not limited due to the factthat it must be grounded or that it must be attached to a suitable powersupply. The present invention recognizes the fact that the greater theratio Q/C the greater the sensitivity of the apparatus, with Qrepresenting the charge on the collector electrodes which is caused bythe electrostatic field and with C representing the capacity between thecollector electrodes.

It is therefore an object 'of the present invention to provide anextremely sensitive electrostatic field measuring apparatus which neednot be grounded and movement of which is not limited by the necessity ofattaching the apparatus to a suitable power supply. With this object inview, the present invention resides in a measuring apparatus in whichthe collector electrodes are in the form of stationary and substantiallyparallel plates, which plates are periodically shielded by means of twoelectrically connecting shielding electrodes which have the same orsimilar shape as the collector electrodes. One advantage of.

the present invention is that such an apparatus need not be grounded butnevertheless is capable of eliminating the influence of interferingfields which are in the vicinity of the area where the measurement isbeing carried out. Additionally, a measuring apparatus according to thepresent invention is considerably more sensitive than existingapparatus.

In various embodiments according to the present invention the measuringelectrodes are periodically shielded by rotating shielding electrodes.In other embodiments the shielding electrodes, which are above and belowthe measuring electrodes, are stationary and these shielding electrodesare periodically connected to each other and insulated from each otherso that the charges formed thereon are neutralized, so that the same endresult is obtained as in the case of rotating electrodes.

The two measuring electrodes are connected to the input of an amplifier,a suitable measuring resistor being connected across the measuringelectrodes. If desired, the variation in the charge on the collectorelectrode and consequently a measurable voltage dependent upon thestrength of the extraneous field can be obtained, instead ofperiodically shielding and unshielding the collector electrodes orinstead of periodically connecting and disconnecting the shieldingelectrodes to and from each other, by providing a rotatable dielectricplate having the same or similar shape as the collector electrodes whichY trodes.

"ice

dielectric plate is arranged between the collector electrodes androtatable relative thereto.

According to another embodiment of the present invention the varyingcharge on the collector electrodes and consequently the measurablevoltage is produced by varying the distance between the collectorelectrodes.

According to one preferred embodiment of the present invention the twomeasuring electrodes are preferably tri angular and are arrangedexteriorly of the axis of the two rotating shielding electrodes, thelatter being so shaped that in one position the measuring electrodes arecompletely covered and in another position completely un covered. Forexample, the shielding electrodes may be in the form of a regularpolygon. The shielding electrodes are arranged in a suitable housingwhich is open on one side but which does not cover the measuring elec-This embodiment has the particular advantage that when the shieldingelectrodes do not cover the measuring electrodes these shieldingelectrodes have practically no disturbing influence upon the fieldwithin which the measuring electrodes are located so that thesensitivity of such an arrangement is substantially higher than that ofexisting apparatus. Also, the sensitivity of such an embodiment isincreased by virtue of the fact that the measuring electrodes are spacedfrom the housing so that the capacitance between the collectorelectrodes is kept particularly small. Additionally, in such arrangementthe unavoidable capacitance between the lead connecting the collectorelectrodes to the input of the amplifier is maintained very small.

According to another embodiment for the present invention the electricmid-point of the resistor connecting the two measuring electrodes isconnected to a screening electrode and the latter, if one is provided,is connected to the carrier of the apparatus if such carrier is onecapable of holding an electrostatic charge which may result in renderingthe measurement obtained by the apparatus inaccurate. Such a carrier maybe in the form of a balloon, an aircraft, or the like. This has theadvantage that the charge on the carrier has no influence upon themeasurement obtained by the apparatus inasmuch as the field produced bythis charge is distributed symmetrically upon the measuring apparatus.Consequently, the apparatus can be used in the vicinity of stationary ormovable components which are capable of retaining electrostatic chargeswhich would otherwise adversely influence a measurement. Thus, accordingto one embodiment of the present invention an additional metallicelectrode is arranged between the two measuring electrodes, whichadditional electrode is connected to the housing as well as to theshielding electrodes. If the voltage produced by the charges upon themeasuring electrodes and the middle electrode across the two portions ofthe resistor are separately amplified and are so connected to themeasuring bridge that they are additive, then a disturbing influenceupon the field to be measured is exerted by the potential upon themiddle electrode only when this potential very materially diifers fromthe potential of the vicinity.

l-Ieretofore an indication of the direction of the field was possibleonly when an auxiliary generator was provided, the impulse of which wasgreatly amplified and was fed together wit-h the measuring impulses to aphase responsive detector. However, according to the above describedembodiment of the present invention, the direction of the field can bedetermined without additional components by the voltages which appearupon the measuring resistance. It a separate rectifier and amplifier isconnected to the individual portions of the resistance, then only one orthe other will operate depending upon the direction of the field. Inthis manner it is possible to determine not only the magnitude of thefield of strengthbut also the direction thereof.

In another preferred embodiment of the present invention the measuringresistance is replaced by a gridcathode path or by two seriallyconnected high ohmic gridrcathodepaths. 1n the latter arrangement amiddle electrode arranged between the two measuring electrodes isconnected to the midle of the two serially connected grid-cathode paths,the latter preferably being in the form of eleotrometer tubes. Asalready set forth above, this middle electrode can be electricallyconnected to the shielding electrodes.

According to another embodiment of the present invention, thecapacitance of the leads connecting the measu-ring electrodes to theinput on the amplifier as well as the input capacitance of the amplifieritself can be compensated for by connecting the measuring electrodes toat least one choke coil and by so selecting the parameters of the thusformed parallel resonant circuit that its resonant frequency is equal tothe indicated frequency at which the measuring electrodes are shieldedand uncovered by the shielding electrodes or the frequency at which thestationary shielding electrodes are charged and discharged. Thisembodiment can be so constructed that the choke coil is parallel to themeasuring electrodes. The choke coil can be tapped in the middle so thatone of the above described arrangements is formed. The sensitivityincreases with increased resonance frequency and when the latter issubstantially the same as the indicated frequency the sensitivity isincreased by a factor of approximately 100. Additionally, thesensitivity is increased inasmuch as the inevitable capacitance of thevarious circuits components is no longer harmful inasmuch as thiscapacitance simply forms part of the total capacitance of the resonantcircuit.

In those embodiments in which the shielding electrodes are stationaryrelative to the measuring electrodes and in. which the shieldingelectrodes are periodically discharge equalization by way of theinsulation under the influence of the electric field is large ascompared to the time constant of a charge equalization which, uponcreation and destruction of an electrostatic field between the shieldingelectrodes, takes place from one measuring electrade to the other by wayof the resistance.

In the above described embodiments a'change in the extraneous fieldbetween the two measuring electrodes is produced by readily controllableconstant means, this field between the measuring electrodes beingproportional to the strength of the ambient extraneous field. Forexample, this is accomplished by periodically varying the distancebetween the electrodes or by periodically introducing a dielectricbetween the measuring electrodes. Alternatively, by shielding themeasuring electrodes from the extraneous field the field whichinfluences these measuring electrodes can be reduced to zero, so that inthis way a field change can be produced which is proportional to theintensity of the extraneous field, so that a voltage dependent upon thechanges is' produced across the measuring electrodes. For suchmeasurements in which the relative changes in the field intensity are ofgreater importance than the absolute value of the extraneous field, itis possible to use embodimentsof the present invention in which theabsolute value of the extraneous field is determined but once at thebeginning of the measuring operation. Afterwards, the individualmeasurements will simply measure the variationswhich the extraneousfield has undergone. This simplified measuring procedure has theadvantage that the periodically moved shielding electrodes may bedispensed with; However, for such measurements it is essential that thetime constant of the measuring resistance between the meascording tothepresent invention;

'pulses.

uring electrodes be large relative to the time interval during which theentire measuring sequence is carried out. Alternatively, thevoltage/time curve of the charge equalization of the measuringelectrodes over the resistance should be known so that the actual valuescan be computed from the measurements obtained. In these last'mentionedembodiments the extraneous field acts constantly upon the measuringelectrodes and only the relatively small voltages which bring about achange of the extraneous field acting upon the measuring electrodes areamplified and indicated, and thereafter added to or subtracted from thefield intensity measured at the beginning of the measurement operation.It has been found that measurements obtained in this manner are adequatefor practical purposes.

In view of the fact that the intensity of the field and consequently themeasurable voltages are relatively small when the apparatus is movedfrom place to place within any particular region, suitable means areprovided by means of which these relatively small voltages produced bythe changes in the extraneous field may more readily be determined. Thismay be achieved by periodically reversing the polarity of the leadsconnecting the measuring electrodes and the resistance. Alternatively,the input tube is modulated with audio-frequency. According to a thirdembodiment of this group field plates are substituted for the shieldingelectrodes and are arranged on opposite sides of the measuringelectrodes, and these field plates are preferably modulated withsawtooth in This achieves substantially the same result as modulatingthe input tube, but it producesthe advantage that the extraneous fieldmay be modulated oppositely, i.e., with a phaseshift of 180. Thissimplifies the construction of the amplifier and the measuring bridge,and additionally, this enables the direction of the field to bemeasured.

The novel features which are considered as characteristic fortheinvention are set-forth in particular in theappended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, Willbe best understood from the following description of specificembodiments when read in'connection with the accompanying drawings, inwhich:'

FIGS. 1 to 5 are schematic representations of several embodimentsaccording to the present invention;

FIG. 6 shows the construction and use of an apparatus according to thepresent invention;

FIG. 7 is a sectional view through the measuring head of the apparatusshown in FIG. 6;

FIG. 8 is a plan view of the measuring head of the apparatus shown inFIG. 6;

FIG. 9 is a schematic diagram of one embodiment of a circuitincorporated in the measuring head;

*FIGS. 10, 10a andlOb are schematic diagrams of in dicating bridgesadapted to be used'in an apparatus ac- FIG. 11 is a schematicdiagrarn ofan embodiment of the present invention capable of giving a phaseresponsive indication;

FI GS. 12a, 12b and schematically illustrate the operation, ofembodiments of t-he present invention tionary shielding electrodes orfield electrodes;

FIG. 14' is a schematic diagram of a circuit adapted to be used inconjunction with the embodiment shown in FIGURE 13 and FIG, 15 shows anadditional embodiment of a circuit adapted to be used ina measuringapparatus according to the present invention.

FIGS: 1 and 1a show an embodiment which is sym- 'metrically'constructed.{Iheapparatus comprises a shaft 1 which is suitably mounted for rotationand which carlies two symmetrical parallel measuring electrodes 2. Theshaft 1 is made of good insulating material. The measuring electrodes 2are encompassed by the shielding electrodes 3 which are likewisesymmetrical relative to each other. The measuring electrodes andshielding electrodes are shaped as shown in FIGURE la so that in oneposition the measuring electrodes are completely covered by theshielding electrodes whereas when the shielding electrodes are rotated90 they free the measuring electrodes so that the latter are completelyuncovered. The individual plates of the electrodes are connected to theends of a resistor 5 by way of slip rings 4, the resistor 5 beingconnected in parallel to the input of an amplifier 6.

When the measuring electrodes are exposed to a field, the same willinduce a charge upon the electrodes. However, there will be no voltagebetween the plates of the electrodes inasmuch as the electrostatic fieldbetween the plates is collapsed by way of the resistor 5. The twomeasuring electrodes are dissimilarly charged. However, when themeasuring electrodes are shielded, the charges induced upon the platespreviously by the extraneous field will equalize themselves so that acurrent will flow through the measuring resistance 5. Thus, a voltagemay be measured across the resistance, and this voltage is a measure ofthe extraneous field, this field, however, no longer acting upon themeasuring electrodes due to the shielding. The shielding electrodes maybe so shaped that a sinusoidal voltage is used across the resistance 5.If the shielding were provided on but one side, the apparatus would haveto be grounded.

The embodiment shown in FIG. 2 differs from that illustrated in FIG. 1only in that the shielding electrodes are movable and the measuringelectrodes 2 are stationary so that it is not necessary to provide anyslip rings which form a source of considerable errorsin measurement.

In the embodiment shown in FIGURE 3 the measuring electrodes 2 areshielded from each other only from time to time in order to establish areference point for the measurement or for regulating the same. To thisend a dielectric plate 7 is arranged between the measuring electrodes 2,the plate and the electrodes having the same shape substantially asshown in FIGURE la. The plate 7 is carried upon the shaft 1 so that theplate may be moved between two positions in one of which it is outsideof the space between the electrodes. With the extraneous field remainingconstant, the electrostatic charge upon the measuring electrodes 2 isgreater when the dielectric plate 7 is between the measuring electrodes2 than when the plate 7 is exteriorly of the space between the measuringelectrodes 2. Consequently, a capacitance current will flow through theresistance 5, the period of this current being equal to twice the speedof rotation of the plate 7 and the amplitude of the current beingameasure of the intensity of the extraneous field.

FIGURE 4 shows an arrangement in which a variation in the distancebetween the measuring electrodes produces a capacitance current throughthe resistance 5. As in the above embodiments, the amplitude of thecurrent is a measure of the intensity of the extraneous field to bemeasured.

In the embodiment shown in FIGS. 3 and 4 the resistance 5 must be veryhigh so that the time constant of the flow of the charges through theresistance 5 is very large, which flow would eventually bring about acollapse of the field between the two measuring electrodes.

In the embodiments shown in FIGS. 1 and 2 the extraneous field actingupon the measuring electrode 2 comes and goes periodically at thatfrequency at which the measuring electrodes are screened. In theembodiment shown in FIGS. 3 and 4 the field prevailing between themeasuring electrodes is changed periodically either by introducing adielectric between the measuring electrodes or by varying the distancebetween them. In each of the embodiments shown in FIGS. 1 and 4 a changeis obtained which is proportional to the absolute value of.

the extraneous field.

In contradistinction thereto, the field acting on the measuringelectrodes 2 in the embodiment of FIGURE 5 is not changed. Instead, thepolarity of the connecting leads between the measuring electrodes 2 andthe resistance, which is shown as being in the form of the grid cathodepath of an electrometer tube, is periodically reversed. The charges onthe electrodes 2 constantly seek to equalize themselves by way of thevery large resistance constituted by the grid-cathode path of theelectrometer tube, and a very small current is permitted to flow so thata voltage can actually be measured between the grid and the cathode. Thetime constant for this discharge process should be as high as possible,such as of the order of one or more hours. The changes of intensity ofthe extraneous field as a function of the location of the apparatus maythusbe determined by measuring the changes in the voltage between themeasuring electrodes 2. In the event the measuring process requires alength of time which is comparable to the time constant of the dischargeprocess, the voltages obtained must be computed into different voltagesby means of a voltage/ time curve. The periodic reversal of polarity ofthe leads between the measuring electrodes and the measuring resistance,which in the illustrated embodiment has been shown as a grid-cathodepath, produces an alternating voltage, so that an A.C. amplifier can beprovided. An A.C. amplifier is far simpler to build and to operate thana DC. amplifier, the latter being required for amplifying the relativelysmall voltage fluctuations which occur at the grid of the electrometertube due to variations in the intensity of the extraneous fielddepending upon the location of the apparatus. This variation in theextraneous field may also be obtained by the embodiment shown in FIGURE5 by providing a rectifier, preferably a full-wave rectifier, connectedbehind the A.C. amplifier.

By virtue of an apparatus according to the present invention, andparticularly due to the symmetrical arrangement of the measuringelectrodes, it is not necessary to ground the apparatus, and itssensitivity is thus materially greater than that of existing apparatus.This increased sensitivity and the fact that the apparatus need not begrounded to earth makes it possible for the apparatus to be used in manyways heretofore impossible. For example, the increased sensitivityenables the apparatus to be used for testing dielectric materials insuch a manner that the material itself is not destroyed. Additionally,the precise field pattern of an atmospheric static field can be examinedvery accurately. A particularly significant use of the present inventionis that a measuring apparatus of the type disclosed herein can be usedfor examining the make up characteristic features of the upper layers ofthe earths surface by measuring irregularities of the electrostaticfield. Moreover, a measuring apparatus according to the presentinvention may be used for measuring the charge on living organisms andfor measuring artificially induced charges for medicinal purposes.

FIGS. 6 to 8 show one embodiment of an apparatus ac-' cording to thepresent invention which possesses the characteristic features of theembodiment shown schematically in FIGURE 2. A measuring head 8 arrangedat the forward end of a rod 9 carries a driving motor (not shown). forthe shaft 1 which carries the shielding electrodes 10, the latter beingin the form of squares. Additionally, the measuring head 8 carries anamplifier. The measuring electrodes 2 are carried by insulating rods 11which are attached to a middle electrode 13, the latter being connectedto the housing 12.- The housing 12 contains the resistance 5, or itsequivalent, as well as an amplifier 6.

The measuring electrodes 2 consist of triangular plates and are soarranged that when the shielding electrodes occupy the position shown inFIGURE 8 the measuring electrodes 2 are completely exposed to theextraneous electrostatic field. When the shaft 1 is rotated 45 themeasuring elec- 7 trodes 2 are completely shielded by the shieldingelectrodes 10.

Ahousing 14 attached to the rear portion of the rod 9 contains themeasuring bridge, and a carrying strap 15 which is attached torthe rod 9at approximately its middle serves to facilitate holding and carrying ofthe entire apparatus; The rod 9 is madeof'insulating'material sothat themeasuring head8 is free to assume the potential'of its immediatevicinity rather than the potential of the operator who w-illbe either atearth potential or at the potential of his immediate" vicinity. Thus,thanks to the relatively large distance between the measuring head 8 andthe operator the-field to be measured by the measuring headB is, for allintents and purposes, uninfiuenced by the operator.

FIGURE 9 shows a suitable schematic diagram of the measuring head 8. Thecircuit includestwo electrometer tubes 17 arranged in common plateconnection, these tubes takingthe place of a resistor the middle ofwhich could be connected to the middle electrode 13. The grids of thesetubes are connected to each other and to the middle'electrode by way ofhigh ohmic resistances 16. The higher the-speed of rotation of theshielding electrodes 10, the lower need be the resistance of theresistors 16. The electrometer tubes 17 are supplied by an-anode battery18 and the anode current is additionally modulated by a transformer 19so that even when the screening electrodes rotate relatively slowly, theamplifier may still operate in its linear zone. The inputto theelectrometer tubes is in phase so that in the bridge circuit which isconnected behind the amplifier circuitthe alternating current across theanodes of the electrometer tubes will have no effect.

Instead only thefluctuations'which will result due to theextraneousfield will be indicated. In order to assure operation of the amplifierinthe' linear zone, the amplifier tubes Ztishould also be connected incommon base connection. As a result, the output resistance of theamplifier, to which the bridge circuit is connected, will be low.

The alternating voltages are amplified separately and are subsequentlyrectified separately as well.

FIGURE 10 shows one embodiment of a circuit of the measuring bridge inhousing 14. The measuring voltages of the two measuring electrodes areagain separately amplified behind the inputpotentiometers 21 by means oftransistors 22, and are then simultaneously rectified by a full waverectifier indicated generally at 23. The thus obtained D.C. serves tocontrol the transistors 24 of the measuring bridge. The measurement isthus particularly sensitive inasmuch as the upper half of the bridge isinve'rsely detuned as the lower half so long as the fieldbetween themiddle electrode 13 and two measuring electrodes 2 is in the samedirection. 7 v

The measurement canbe read. from an indicating instrument 25, or anacoustic indication can be given. Such an acoustic indicator can beattached to binding posts 26 and 27 by way of a differential connectionin which an indication of the alternating voltage of the modulation issuppressed. FIGURES 10a and 1012 show such connections. The resistances28 serve to balance the bridge. If desired, an additional indicatinginstrument can be connected to the binding post 29 and 30.

' FIGURE 11 shows a furtherembodiment of a circuit adapted to beconnected to the measuring electrodes. The

input circuit behind the electrodes is the same as in FIG-' thus amplifythe high frequency of the generator 31.

The grid potential of the electrometeritube 17 is higher than that oftheelectrometer tube I17, or vice versa, de= pendent upon direction ofthe field, and. the'magnitude ofth'e phase shiftrelative to the.generator frequency is changed by the cooperationbf' the two tubes33and'34i a measuring bridge, the magnitude of the phase shift being Thevoltages 7 taken from the electrorncter tubes of the measuring elec- Vtrodeszz are fed tothe grids of'the tubes 33vand 34 and 1 a ($8The-phase of the frequency generatedby the generator-31. iscomparedwiththe shifted frequency supplied: to the a measure of thefield-intensity and the direction of the shift being a measure of thedirection of thefield; The indicating instrument 36 thus shows not onlythe strength of the field being measured but also its direction. In thisembodiment rectification in the bridge is carried out by means of a fullwave rectifier tube 37.

FIGURES l2 and 13 schemaitcally show additional circuits for measuringthe field intensity of an extraneous field.

FIGURE 12 shows two measuring electrodes which are wellinsulated fromeach other and which are mounted'on the measuring head in spacedrelation relative to'each between the electrodes 2,'which field isdependent upon the extraneous field to be measured, collapses due to thedischarge through the resistor 5'. This displacement or capacitancecurrent is then measured, either by any one of the above describedarrangements or in any other suitable manner. The connection 38 is thenimmediately opened and the two platesof the measuring electrodes willthen again be charged to that extent to which they were charged beforethe charges-were equalized'by way of'the conductor 38 (FIG. 12c) so thatthe electrodes 2 are once again electrically neutral relative to eachother. This can be accomplished withthe necessary degree of accuracy bymeans of electronic switches, it-being essential that the connection ofthe plates, the equalizing of the charges, the opening of the connection38 and the neutralizing of the electrically insulatedplates 32 as aresult of charging thereof be accomplished very rapidly one after theother and that the timeinterval which isnecessary for this procedure be.very small as compared to the time interval in which the steps followeach other, i.e., the time interval between the carrying out ofindividual measurements. To this endthe resistance of the resistor 5 canbe maintained relatively small so that the discharging process will notbe encumbered by any large time constant. An amplifier is connected tothe resistance 5 in the manner described above, and inasmuch as thevoltage which appears across the resistance 5 and which is amplified bythe amplifier is a measure of the amplitude of the capacitance current,-a part of the amplified impulse is used to neutralize the measuringelectrodes 32 which are again insulated from each other. For veryprecise measurements it is essential that at the beginning of the abovedescribed cycle the plates 2 be electrically absolutely neutral relativeto each other. This may most easily be accomplished by placing theplates 2, from time to time, ina cage and by electrically connecting theplates with the inside of this cage; In order to accomplish this,movable screeningelectrodes may be provided on opposite sides of themeasuring electrodes 2, as set forth above, which electrodes may,whenever required, be turned so as to cover the plates 2. Additionally,the screening electrodes may beprovided with a suitable collector brushor the like so that when the shielding electrodes cover the measuringelectrodes, the outer surfaces of the latter are electrically connectedto the inner surfaces of the screening electrodes.

Alternatively, two pairs of electrodes may be provided instead ofbut onepair. Such an arrangement, which is shown in FIGURE 13, has theadvantage that the switching means for connecting the twomeasuringelectrodes and the switching meansfor measuring the field can bemaintained completely separate from each other. 7 Thus; an apparatusaccording to FIGURE 13 incorporates in 7 addition to the two measuringelectrodes 2 two field electrodes 3? which areinsulated from 'eachotherand are so arranged as to be-capableof'shielding or screening themeasuring electrodes 2 completely. As set forth above,

the measuring electrodes- 2 are connected. to:- a resistor or to thegrid-cathode paths of electrometer tubes, and the input of the amplifieris connected across the resistance. Assuming now that the fieldelectrodes have been rendered electrically neutral relative to eachother, such as by placing the electrodes in a cage, the extraneous fieldpenetrates through the plates 39 and acts upon the measuring electrodes2. Furthermore, it is assumed that in FIGURE 13 the extraneous field tobe measured has changed between the instant shown in FIGURE 13a and theinstant shown in FIGURE 13b. In the instance shown in FIGURE 13b, theouter field electrodes 39 are connected to each other by means of anelectronic switch so that the field between the electrodes 39 collapsesso that a capacitance current flows not only through the connector '40into connecting the field electrodes 39 but also through the resistorwhich interconnects the measuring electrodes 2. The voltage producedacross the resistor 5 is amplified and the impulse taken from the outputof the amplifier is a measure of the intensity of the extraneous field.This amplified impulse is used on the one hand for indicating purposesand on the other hand for bringing a charge on the now insulated fieldplates 39 which correspond in magnitude to the collapsed shield, so thatthese plates are once again electrically neutral relative to each other.Discharging may be accomplished by way of electronic switching means.

FIGURE 14 is a schematic representation of a circuit adapted to be usedin conjunction with the arrangement shown in FIGURE 13. Theinterconnection of the measuring electrodes 2, the middle electrode 13and the electrometer tubes 17 and 17' is the same as in the abovedescribed embodiments, Whereas the shielding electrodes 13 have beenreplaced by field electrodes 39. Each of the field electrodes isconnected to the middle electrode 13 by way of two parallel tubes 41 and42. The cathode of each tube 41 is connected to one of the fieldelectrodes 39 and the plate of each tube 41 is connected to the middleelectrode 13. The tubes 42 are inversely connected, the plates of eachof the tubes 41 being connected to one of the field electrodes andcathode of each tube 41 being connected to the middle electrode. Thecathodes of these tubes are heated by small heating batteries. Theheating until emission, however, is the result of an impulse which isproduced in the switching circuit 43,

preferably by a thyratron, which impulse is inductively transmitted tothe heating conductors of the individual tubes 41 and 42. The tubes 41and 42 conduct in this heated stage so that a voltage between the middleelectrodes 13 and the field electrodes 39 can equalize itself.

'When the field electrodes 39 carries a positive voltage,

equalization takes place by the way of the tubes 42, whereas when thefield electrode 39 carries a negative potential, equalization takesplace by way of tube 41. The tubes 41 and 42 cease to conduct at the endof the heat impulses due to the cooling of the cathodes, so that thefield electrodes are once again insulated from each other as well asfrom the other components. The field between the field electrodes 39collapses during equalization which takes place as a result of the shortcircuit constituted by the parts 41, 42 and 43, and a voltage impulse isproduced across the measuring electrodes 2,

which impulse is amplified in the amplifiers 44,- 44 and is supplied tothe measuring bridge by way of the leads I, II, and III. However, a partof the impulse is fed to delay elements 46 and 46 by way of connectors45 and -45', which elements 46 and 46' are so selected that the impulseleaves the elements only whenthe tubes 41 and 42 have been renderednon-conductive so that the field electrodes 39 are isolated from eachother. The impulse leaving the delay elements 46, 46' is fed to the gridof one of the tubes which charges the field electrode 39 to the extentto which this electrode was charged before the charges were equalized byway of the tubes 41 and 42, so that the field electrodes 39 is onceagain electrically neutral.

The arrangement must be such that the positive or negative charge can beapplied to either of the electrodes 39. This must be so inasmuch as itis the direction of the field which will determine which of the twofield electrodes will, after the short-circuiting and opening of theshort-circuit, be negatively charged and which electrode will bepositively charged. To this end a circuit is provided to which the gridsof the tubes are connected. The impulse leaving the delay element 46 iseither positive or negative, depending upon the direction of the field.If the pulse is positive, it passes through the rectifier 47 and theresistance 48 to the middle electrode 13, in which case the grids of thetubes 49 receive a positive potential so as to render the tubesconductive, and this, in turn, causes a negative charge to be suppliedto the field electrode 39. If the impulse leaving the delay element 46is negative, it passes through the rectifier 47' and the resistance 48'to the middle electrode 13. An inverter 50 is provided which is capableof changing the sign of the impulse and this produces a positivepotential on the grid of the tubes 49 so that these tubes are renderedconductive. In this way, a negative charge is drawn from the fieldelectrode 39 so as to render the same positively charged. A pulseleaving the delay element 46',

l which pulse has a sign opposite that of a pulse leaving the delayelement 46, produces a similar result.

The charges supplied to the field electrodes 39 are taken from the platebatteries 51. Suitable switch means (not shown) may be provided formaking sure that the charges supplied to the field electrodes 39 areproportional to the impulses taken from the measuring electrodes 2.

FIGURE 15 shows another embodiment according to the present inventionwhich differs from the previously described embodiments, wherein uponeach measurement the entire extraneous field is varied by an amountproportional to its strength so that the field intensity changes may bemeasured and given indication of the field strength, in that in theinstant embodiment the extraneous field remains undisturbed and onlythat amount is measured by which the field intensity changes from placeto place from time to time. These changes are relatively small andproduce very small but constantly changing direct current components.Such current components are difiicult to amplify, and in order toovercome this disadvantage suitable means are provided for modulatingthese direct current components, thereby avoiding the difficultiesinherent in direct current amplification. Such modulation can take placeeither in the measuring circuit or in the input circuit of theamplifier. However, in the illustrated embodiment the extraneous fieldis modulated by a pulse field. The field electrodes 39 are connected toa pulse generator 52 which impresses sawtooth pulses upon the fieldelectrodes 39 by way of capacitor 53. The modulation takes place inopposition, i.e., in one half of the measuring apparatus the modulationis in the direction of the field whereas in the other half it is in theopposite direction. In this way the modulation is eliminated in'themeasuring bridge.

In those embodiments in which a middle electrode 13 is arranged betweenthe measuring electrodes 2, the voltage produced between the middleelectrode and one of the measuring electrodes as well as the voltageproduced between the middle electrode and the other measuring electrodecan be amplified and fed to the bridge. In the other embodiments of thepresent invention it suffices if the voltage between the middleelectrode and one of the measuring electrodes during changing of theextraneous field is measured and amplified. The switching circuit canthen be so selected that depending upon the di- It will be understoodthat each of the elements described above, or two or more together, mayalso find a '1 1 useful application in other types of measuringapparatus differing from the types described above.

While the invention has been illustrated and described as embodied in ameasuring apparatus for measuring the field intensity of an extraneousfield, it is not intended to be limited to the details shown, sincevarious modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further anal sis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a measuring apparatus for measuring an electrostatic field, incombination, a pair of capacitor plates; shielding means operativelyassociated with said capacitor plates, said plates and shielding meansbeing movable relative to each other between a shielded position whereinsaid plates are protected against the influence of said electrostaticfield and an unshielded position wherein plates are exposed to saidelectrostatic field; and electrical resistance means interconnectingsaid capacitor plates, whereby when said plates are unshielded anelectrostatic charge will, due to the influence of said electrostaticfield, accumulate on said plates which electrostatic will, when saidplates are then shielded, cause an electric current of flow through saidresistance means, said electric current being a measure of the intensityof said electrostatic field.

2. In a measuring apparatus for measuring an electrostatic field, incombination, a pair of capacitor plates; shielding means oper-ativelyassociated with said capacitor plates, said plates and shielding meansbeing movable relative to each other between a shielded position whereinsaid plates are protected against the influence of said electrostaticfield and an unshielded position wherein plates are exposed to saidelectrostatic field; electrical resistance means interconnecting saidcapacitor plates, whereby when said plates are unshielded anelectrostatic charge will, due to the influence of said electrostaticfield, accumulate on said plates which electrostatic will, when saidplates are then shielded, cause an electric current to flow through saidresistance means, said electric current being a measure of'the intensityof said electrostatic field; and means for measuring the voltage acrosssaid resistance means caused by the fiow of said electric currenttherethrough.

3. The combination defined in claim 2, and means for periodically movingsaid plates and shielding means relative to each other between saidshielded and unshielded position. I 4. The combination defined in claim2wherein said plates are stationary and said shielding means are movablerelative thereto.

5. The combination defined in claim 2 wherein said angular position theycompletely uncover said plates.

7. The combination defined in claim 4 wherein said plates and saidshielding means are constructed sym metrically.

12 said plates'and shielding means are so shaped that in one angularposition of said plates they are completely covered by said shieldingmeans and that in another angular position they are completely uncoveredby said shielding means.

9. The combination defined in claim 8 wherein said plates and shieldingmeans are constructed symmetrically.

10. The combination defined in claim 2 wherein said shielding includes apair of electrically connected shielding plates arranged on oppositesides of said capacitor plates.

11. The combination defined in claim 6 wherein said platfes are arrangednon-symmetrically relative to said shat.

12. The combination defined in claim 11 and support means supportingsaid capacitor plates and said shielding means, said capacitor platesbeing substantially triangular in shape projecting from said supportmeans and said shielding means being in the form of regular polygonalplates arranged on opposite sides of said capacitor plates and rotatablewith said shaft between said shielded and unshielded positions.

13. The combination defined in claim 12, and connecting meanselectrically connecting the electrical midpoint of said resistance meansto said shielding means and to said support means.

14. The combination defined in claim 13 wherein said measuring meansinclude two measuring components connected to each electrical half ofsaid resistance means, respectively, whereby the direction of saidelectrostatic field may be determined.

15. The combination defined in claim 13, and an additional platearranged between capacitor plates, said additional plate beingelectrically connected to said electrical mid-point of said resistancemeans.

16. The combination defined in claim 13 wherein said electricalresistance means is constituted by the gridcathode path of anelectrometer tube.

17. The combination defined in claim 13, and choke coil means connectedto said capacitor plates and forming a resonant circuit therewith, theparameters of said circuit being so selected that the resonant frequencythereof is substantially equal to the frequency at which said capacitorplates are shielded and unshielded.

, 18. The combination defined in claim 17 wherein said choke coil meansare arranged symmetrically relative to said electric mid-point of saidcapacitor plates.

19. The combination defined in claim 13 wherein said electricalresistance means includes the grid-cathode paths of at least twoelectrometer tubes arranged in common plate connection, the point commonto the plates of said electrometer tubes being connected to theelectrical midpoint of said capacitor plates.

20. The combination defined in claim 13, and means for-modulating thevoltage across said resistance means with an alternating voltage.

21. The combination defined in claim 19 wherein said grid-cathode pathsof said electrotneter tubes are so ar- 8. The combination defined inclaiin'S wherein said ranged that a capacitance current may flow throughbut one of them, whereby the direction of said electrostatic field maybe determined.

22.-The combination defined in claim 21 wherein the currents: flowingbetween said additional plate and each of said capacitor plates areseparately amplified and rectified. e e i 23. The combination defined inclaim 22, and bridge means for measuring the separately amplifiedandrectified currents.

24. The combination defined in claim ZI' wherein said measuring meansinclude acoustic indicating means.

25. Thecounbination defined in claim. 24,- and differential switchingmeans operativelyconnected'to said acoustic indicating means. e

(References on following page References Cited in the file of thispatent UNITED STATES PATENTS Kirby et a1. June 15, 1926 Murray Sept. 6,1927 5 Gunn July 25, 1933 Siegenheim Feb. 6, 1940 Schweitzer Feb. 18,1941 14 Stevens Aug. 14, 1945 Carter et a1. Dec. 9, 1947 Gunn Sept. 14,1948 Herold July 17, 1951 Havenhil-l et a1 Feb. 26, 1952 Graham Dec. 22,1953 Kaufman Dec. 3, 1957 Gunn Jan. 21, 1958

